ASPECTOS FLORAIS E REPRODUTIVOS DE Psychotria capitata RUIZ & PAVON (RUBIACEAE), UM CASO DE DISTILIA TÍPICA NO CERRADO

BREEDING SYSTEMS AND POLLINATION OF THE PSYCHOTRIA CAPITATA RUIZ & PAVON (RUBIACEAE): A CASE THE TYPICAL DISTYLY IN CERRADO: The phenotypic integration observed in flowers is an evolutionary strategy that aims to increase the pollen flow between individuals, favoring the crossing and maintenance of genetic variability. This success is directly related to the floral structure, such as hermaphroditism, and to the behavior of visitors, and can generate conflicts between the floral structures, being selected characteristics that reduce this conflict and amplify the pollen flow, as is the case of heterostyly. The objective of the study was to describe the floral characteristics, the reproductive system, and pollination in Psychotria capitata Ruiz & Pavon (Rubiaceae). For this purpose, the floral structures were measured and observed, controlled crossings were carried out, the floral visitors were observed and the nectar production was evaluated. Psychotria capitata is a typical dystylic species, shrub with a maximum height of 3 meters, with high rates of reciprocal hercogamy between the floral morphs. It has white tubular flowers, visited by a wide range of insects, including moths, bees, wasps and flies. There was higher fruit formation in intermorphic cross-pollination (> 60 %) and lower formation in intramorphic (< 20 %) and self-pollination (< 15 %), characterizing self and intramorphic incompatibility. These data were confirmed by the non growth of pollen tubes in self-pollinated pistils and intramorphic pollinators. Blooming is annual, and occurs between the months of October and January, with peak blooming in November and December. The reproductive data evaluated are similar to other Rubiaceae species in the Cerrado forest sub forest. These data enrich the reproductive knowledge of Rubiaceae's sub-forest species, so important for the maintenance of fauna in forest fragments.

Distance Dependent Contribution of Ants to Pollination but Not Defense in a Dioecious, Ambophilous Gymnosperm

Dioecious plants are obligate outcrossers with separate male and female individuals, which can result in decreased seed set with increasing distance between the sexes. Wind pollination is a common correlate of dioecy, yet combined wind and insect pollination (ambophily) could be advantageous in compensating for decreased pollen flow to isolated females. Dioecious, ambophilous gymnosperms Ephedra (Gnetales) secrete pollination drops (PDs) in female cones that capture airborne pollen and attract ants that feed on them. Plant sugary secretions commonly reward ants in exchange for indirect plant defense against herbivores, and more rarely for pollination. We conducted field experiments to investigate whether ants are pollinators and/or plant defenders of South American Ephedra triandra, and whether their contribution to seed set and seed cone protection varies with distance between female and male plants. We quantified pollen flow in the wind and assessed the effectiveness of ants as pollinators by investigating their relative contribution to seed set, and their visitation rate in female plants at increasing distance from the nearest male. Ants accounted for most insect visits to female cones of E. triandra, where they consumed PDs, and pollen load was larger on bigger ants without reduction in pollen viability. While wind pollination was the main contributor to seed set overall, the relative contribution of ants was distance dependent. Ant contribution to seed set was not significant at shorter distances, yet at the farthest distance from the nearest male (23 m), where 20 times less pollen reached females, ants enhanced seed set by 30% compared to plants depending solely on wind pollination. We found no evidence that ants contribute to plant defense by preventing seed cone damage. Our results suggest that, despite their short-range movements, ants can offset pollen limitation in isolated females of wind-pollinated plants with separate sexes. We propose that ants enhance plant reproductive success via targeted delivery of airborne pollen, through frequent contact with ovule tips while consuming PDs. Our study constitutes the first experimental quantification of distance-dependent contribution of ants to pollination and provides a working hypothesis for ambophily in other dioecious plants lacking pollinator reward in male plants.

Low Outcrossing from an Apple Field Trial Protected with Nets

Regulatory compliance of experimental releases into the environment of not yet approved genetically modified plants often requires implementation of measures to reduce the dispersal of reproductive material. To study the impact of nets on pollen flow in an experimental field site in Switzerland, non-GM apple varieties ‘Ladina’ and ’Nicogreen’ were planted inside and outside a netted plot, respectively. Seeds harvested from mature fruits were germinated and the paternal variety of the seedlings was determined using simple sequence repeat (SSR) molecular markers. We demonstrate that pollination frequency from trees inside the netted plot to trees outside over a two-year (2018 and 2019) study of 4500 seedlings is 0.6% (26 seedlings). Moreover, these outcrossing events decreased with increasing distance from the pollen donor. Over the study period, we found on average 0.9%, 0.5%, 0.4% and 0.09% of the seedlings derived from apples of ‘Nicogreen’ trees at 8 m, 15 m, 72 m and 117 m being generated by fertilisations of ‘Ladina’ pollen, respectively. In comparison, 48.3% (2018 season) and 75.1% (2019 season) of examined ‘Ladina’ seedlings in the netted plot originated from ‘Nicogreen’ tree pollen outside the netted plot. The results suggest that insect netting is effective in minimizing egress of apple pollen from an experimental site and that the likelihood of outcrossing is reduced further (<0.1%) when there are no compatible apple trees within a radius of 100 m of the pollen donor. These data are important for biosafety research/regulation to aid understanding of pollen flow in experimental field sites.

Pollen Flow of Winter Triticale (x Triticosecale Wittmack) Investigated with Transgenic Line Expressing β-Glucuronidase Gene

A transgenic winter triticale line expressing the uidA gene, encoding β-glucuronidase, was used to assess the pollen flow in field experiments over two consecutive vegetation seasons in central Poland. The experimental design included two variants of mixed transgenic and non-transgenic lines. Pollen grains were collected using passive traps located at 0, 10, 30, 60 and 85 meters from the transgenic line. GM pollen grains were detected histochemically by staining with x-Gluc. A positive effect of temperature increase, as well as the strength and direction of the wind on the number and spread of pollen grains was observed. Regardless of the experiment year and variant, only few pollen grains were observed at a distance of 85 m. In the first year of the study the amount of pollen grains at 85 m was 300-fold lower than at the source and 140-fold lower in the second year. The number of transgenic pollen grains was two times lower when the field with the transgenic triticale was surrounded by a non-transgenic line, compared to an empty field. On the basis of the obtained results, we suggest 100 m as the distance for triticale pollen migration, although longer flight incidents are possible in extreme atmospheric conditions.

Frequent coexistence of closely related tree species on a small scale in temperate evergreen forests in Japan

Understanding how biotic interaction affects species composition and distribution is a major challenge in community ecology. In plants, negative reproductive interaction among closely related species (i.e., reproductive interference) is known to hamper the coexistence of congenic species. Since the magnitude of reproductive interference in plants depends on pollen flow distance, we hypothesized that the coexistence of congeners on a small spatial scale would be less likely to occur by chance but that such coexistence would be likely to occur on a scale larger than pollen flow distance. In the present study, we tested this hypothesis using spatially explicit woody plant survey data. Contrary to our prediction, congenic tree species often coexisted at the finest spatial scale and significant exclusive distribution was not detected. Our results suggest that cooccurrence of congenic tree species is not structured by reproductive interference, and they indicate the need for further research to explore the factors that mitigate the effects of reproductive interference.

The effect of the buffer zone on the maize pollen flow in mixed crops

Field experiments were carried out to study the effect of the buffer zone length and wind direction on the crossover frequency between the donor and recipient of maize pollen.

Gene flow among wild and cultivated common walnut (Juglans regia) trees in the Qinling Mountains revealed by microsatellite markers

Patterns of gene flow and gene introgression can be used to assess the risk of genetic pollution of wild forest trees from widespread cultivated trees. A comprehensive understanding of the genetic relationships and levels of gene flow among wild and cultivated common walnut (Juglans regia) has become an urgent issue. Using twelve microsatellite markers, we investigated the genetic diversity and gene flow between cultivated and wild trees of J. regia in the Qinling Mountains, China. A high level of genetic variation was detected in both cultivated and wild trees. The mean number of alleles per locus was 17.5. Observed heterozygosity (HO) and expected heterozygosity (HE) were 0.777 and 0.800, respectively. Pollination of mother trees was not by nearest neighbors, and a paternity of 60.7% of offspring evaluated could not be assigned to a local, sampled tree. Pollen flow from cultivated trees to wild trees was infrequent (5.4%), and selfing rates ranged from zero to 25.0%. Male parents were located from 0 to 1005 m from their female partners, with an average pollination distance of 285.1 m. These results are discussed in light of the cultivated species' diversity, outlining the frequent spontaneous genetic contributions from the wild to the cultivated compartment. In addition, the pollen flow parameters provide useful information about the dynamics of pollen movement within J. regia populations.